Air pollution in form of particulates is a major concern in the world today and the amount of particulates in the air is increasing in many places. Some particulates occur naturally in the air, originating e.g., from volcanos, dust storms and forest/grassland fires. Some particulates are caused by human activities, such as burning of fossil fuel and industrial processes. Increased levels of particulates in the air are linked to several health hazards.
The levels of particulates in the air may be particularly high in large cities with many inhabitants, vehicles and industries. Legislation in some countries relates both to the emission allowed for a certain type of pollution and for the ambient concentration of particulates. For example, the European Union has established the European emission standards, which include limits for particulates in the air. Particles with a diameter of 10 micrometers or less are often referred to as PM10 and particles with a diameter of 2.5 micrometers or less are often referred to as PM2.5.
Due to the health effects of particulate matters, many attempts to reduce the amount of particulates in the air have been made. However, it is still desirable to further reduce the amount of particulates in the air.